1. FIELD OF THE INVENTION
The present invention relates to a flow control device and more particularly to a flow control device for controlling the flow rate of air passing through a by-pass air passage in an intake system of an internal combustion engine.
2. DESCRIPTION OF THE PRIOR ART
Heretofore, in flow control devices of this type there has been used a stepping moror 10 as an actuator, as shown in FIG. 1. With forward and reverse rotations of a rotor 16 of the motor 10, a shaft 80 reciprocates along the axis thereof.
A front end portion of the shaft 80 is positioned within a by-pass air passage 81, and a valve body 82 is provided on the shaft. The valve body 82 moves in contact with or awa from a valve seat 83 provided in the passage 81 in accordance with a reciprocating motion of the shaft 80. With this movement of the valve body 82, the flow path area of the passage 81 increases or decreases to control the amount of air to be supplied.
In the case where two or more by-pass air passages are required, there has been proposed a construction wherein a plurality of valve bodies for controlling the flow rate of air in those by-pass air passages are mounted on the shaft of a single stepping motor. With this construction, the flow rate control for by-pass air is simplified and the control accuracy is improved.
In the case where two or more valve bodies are provided on the shaft of a single stepping motor, the shaft is lenthened as compared with the case where a single valve body is provided on the shaft. As a result, the shaft is apt to vibrate accordingly, and upon exertion of a large external force on the shaft, the valve bodies may be repeatedly brought into contact with the respective valve seats in the by-pass air passages, resulting in that the valve bodies or the valve seats are worn out and the by-pass air flow rate controlling accuracy is deteriorated.